Distancia entre cidades
1.
matrix.ex = matrix(,4,4)
cidades = ("Atenas", "Madri", "Paris", "Estocolmo")
colnames (matrix.ex) = cidades
rownames (matrix.ex) = cidades
matrix.ex [lower.tri(matrix.ex)]= c(3949, 3000, 3927, 1273, 3188, 1827)
matrix.ex

2.
eurodist

Criando um data frame
1.
cor= c("Claro", "Escuro")
dieta= c("A", "B", "C")
var= c(0.1, 1.1, 3.7, 5.7, -1.2, -1.5, 3.0, -0.4, 0.6, 1.5, -0.1, 2.0, 0.6, -3.0, -0.3, -0.2, 0.3, 1.5)
dataframe = data.frame(rep(cor,each=9), rep(dieta,each=3, times=2), var, check.names=FALSE)
colnames(dataframe)= c("Cor","Dieta","Var")

2.
tapply (dataframe$Var, INDEX=dataframe$Dieta, FUN=mean)
tapply (dataframe$Var, INDEX=dataframe$Cor, FUN=mean)

Criando uma Matrix
1.
matrix.ex3 = matrix(rnorm (15, 10, 3.6), ncol=5)
2.
rownames (matrix.ex3) = paste("L",1:3)
colnames (matrix.ex3) = paste("C",1:5)
3.
medias = c(apply(X=matrix.ex3, MARGIN=2, FUN=mean), apply(X=matrix.ex3, MARGIN=1, FUN=mean))
vars = c(apply(X=matrix.ex3, MARGIN=2, FUN=var), apply(X=matrix.ex3, MARGIN=1, FUN=var))
medvar.matrix = data.frame(medias, vars)

Lendo e Salvando seus dados
1.
summary (BIO3)
summary (BIO7)
summary (BIO8)
summary (BIO12)
summary (BIO13)
summary (BIO18)
2.